RFR: Update Readme with macOs specifics [v2]

Tue Mar 29 11:16:46 UTC 2022

On Tue, 29 Mar 2022 11:08:54 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> I hesitated to add this link since I don't if this ok to link to individual builds, even if this is Aleksey Shipilëv.
>
> Sorry, I think it's better not to have the link (I should have made that clearer).

No problem, that was what I assumed there.

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PR: https://git.openjdk.java.net/jextract/pull/10